1. Field of the Invention
The present invention relates to a multi-layer material having gas barrier properties and high heat resistance, and a resin composition to produce a molding having such gas barrier properties and high heat resistance. More particularly the present invention relates to a multi-layer material and a resin composition to produce a molding (especially containers) which can be transported at ambient temperature, because retort sterilization (high temperature steam) is possible and can be stored for a long period of time, and further which has such high gas barrier properties as to permit heating directly by boiling, or in an electric range or a grill oven (220.degree. to 240.degree. C.) without transferring its contents (food) into another container.
2. Description of the Related Arts
Various resin containers are on the market, advertizing that the contents placed in the containers, after refrigeration transportation, can be heated by boiling, or in an electric range or a grill oven (not more than 220.degree. C.) without transferring the contents into another container. Most of these containers are made of crystalline thermoplastic resins such as polyester (C-PET), polypropylene and poly(4-methylpentene). If these containers are put in grill ovens or oven toasters presently used in homes, problems such as distortion of the container often occur because the temperature rises above the temperature to which the containers can withstand. It has therefore been desired to develop a container which can overcome the above problems and which has excellent heat resistance, satisfying the requirements of the market.
A multi-layer material having a general-purpose polystyrene (atactic) layer and a saponified product of an ethylene-vinyl acetate copolymer layer (EVOH) laminated onto each other is well known (Japanese Patent Application Laid-Open Nos. 46281/1979, 107337/1985 and 26072/1985). This type of multi-layer material is widely used in food containers because it has the high moldability and the high transparency inherent in the general-purpose polystyrene and the gas barrier properties inherent in EVOH. This multi-layer structure, however, cannot be used, for example, in a microwave oven or an oven range because it has low heat resistance.
Compounding the general-purpose polystyrene and EVOH is also known as described in, for example, Japanese Patent Application Laid-Open No. 75239/1975. Although this composition shows improvement in hygroscopicity, oil resistance and gas barrier properties to a certain extent, mechanical characteristics are insignificantly improved and moreover heat resistance is low. Thus the composition cannot be used in, for example, microwave oven or oven ranges.